NO.sub.x can be controlled by minimizing its formation and/or causing it to chemically react with chemicals to produce less objectionable compounds and elements. The formation of NO.sub.x is primarily determined by oxygen availability, peak temperature and residence time at high temperatures.
With a homogeneous charge of air/fuel one can minimize formation of NO.sub.x by causing combustion under oxygen starved conditions, but under those conditions objectionable amounts of CO and HC are produced and so steps should be taken to minimize those compounds in an efficient manner (see U.S. Pat. No. 3,877,229 issued to the instant inventor).
With a homogeneous charge at or near stoichimetric, little can be done with peak temperature and residence time at high temperature as a means to minimize formation of NO.sub.x so one is forced to cause the NO.sub.x to be reacted with other chemicals for minimizing the objectionable compound. One manner for producing such NO.sub.x reaction is the well known catalytic exhaust, reactor and another manner for causing NO.sub.x reaction is by mixing the NO.sub.x with HC under proper temperature and oxygen starved conditions as described in copending application Ser. No. 449,391 filed Mar. 8, 1974 by the instant inventor. When employing a homogeneous charge of air/fuel at or near stoichimetric, regardless of which manner of NO.sub.x reaction is employed, one must take additional steps to minimize HC and CO as exhaust pollutants.
Although significant results in the reduction of NO.sub.x, HC and CO exhaust pollutants have been achieved in engines having homogeneous charge of air/fuel at or near stoichimetric, it appears that the goals for pollution control will be extremely difficult, if not impossible, to achieve. Therefore, substantial interest has been recently shown in the use of stratified charge as a means for pollution control.
Many approaches which have been taken for creating stratified charge have been referred to as "prechamber stratified charge engines". A recent review of many of the approaches will be found in the publication entitled "Evaluation of Prechamber Spark Ignition Engine Concepts" by the Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C., dated February 1975 (EPA - 650/2/75-D23). Another group of prior approaches for creating stratified charge employs introducing a relatively fuel-lean air/fuel mixture by way of the conventional carburetor-manifold as the main cylinder charge and introducing fuel or a relatively fuel-rich air/fuel mixture in such a manner as to create a readily ignitable layer at or near the spark plug. Examples of such systems are presented in U.S. Pat. Nos. 3,504,681 to H. Winkler; 2,121,921 to M. Mallory; 2,242,990 to T. E. Brown; 3,238,930 to E. A. VonSeggern et al.; 3,270,721 to L. Hideg, et al.; 3,315,650 to I. N. Bishop et al.; and 3,318,292 to L. Hideg. Still another group of prior approaches for creating stratified charge employs the conventional carburetor system to introduce a stoichiometric air/fuel mixture to the combustion chamber and employs a source of air or relatively fuel-lean air/fuel mixture which is positioned in the area immediately above the piston in the combustion chamber. Examples of such systems are U.S. Pat. Nos. 3,170,445 to Folche; 3,364,911 to Baudry et al.; and 1,505,697 to Campbell.
Since all of the above noted approaches involve the creation of the stratified charge within the combustion chamber rather than pre-forming some or all of the charge prior to delivery to the combustion chamber, they involve complex controls and require design and manufacturing changes to the engine which are costly.
In accordance with the invention disclosed in my copending patent application Ser. No. 610,420, filed Sept. 4, 1975, the need for complex controls and changes to the engine are avoided since the intake manifold is provided with a source of air which is so positioned and proportioned that while the intake valve of the cylinder is closed, air is introduced into the manifold in such a manner as to create within the manifold a pocket of relatively fuel-lean fuel/air mixture.
It should be noted that in prior approaches to stratified charge, the charge is relatively fuel rich or stoichiometric in the vicinity of the spark plug and relatively fuel lean in the vicinity of the piston. With such a form of stratified charge, one can adjust the air/fuel mixture and total quantity of each of the two parts of the charge to minimize the formation of NO.sub.x and CO, however when such is done, there is a probability that the exhuast will contain excess amount of HC under such operating conditions as idle, deceleration, acceleration, and/or cold start.
To control NO.sub.x pollution in the exhaust of internal combustion engines, it has become common practice to incorporate what is known as exhaust gas re-circulation (EGR). In such systems, a portion of the exhaust gases from the exhaust manifold are passed through a control valve and combine with the carburated fuel/air mixture at a point immediately below the throttle plate and the control valve responds to intake manifold pressure. In such a system the carburated fuel/air mixture is uniformly diluted with exhaust gas and the amount of uniform dilution of a given cylinder charge varies with the intake manifold pressure. Examples of such an EGR system are disclosed in U.S. Pat. Nos. 3,625,189 to Myers, 3,809,039 to Alquist, 3,908,618 to Tange, et al. and 3,941,105 to Yagi, et al.